Acid hahdes

Acidic hahde catalysts used in chloromethylation include (44) ZnCl, ZnCl2 + AlCl, SnCl, SnCl, AlCl +ketones, AlCl + pyridine, AlCl ... 

Other Borohydrides. Potassium borohydride was formerly used in color reversal development of photographic film and was preferred over sodium borohydride because of its much lower hygroscopicity. Because other borohydrides are made from sodium borohydride, they are correspondingly more expensive. Generally their reducing properties are not sufficiently different to warrant the added cost. Zinc borohydride [17611-70-0] Zn(BH 2> however, has found many appHcations in stereoselective reductions. It is less basic than NaBH, but is not commercially available owing to poor thermal stabihty. It is usually prepared on site in an ether solvent. Zinc borohydride was initially appHed to stereoselective ketone reductions, especially in prostaglandin syntheses (36), and later to aldehydes, acid haHdes, and esters (37). 

Ketene Insertions. Ketenes insert into strongly polarized or polarizable single bonds, such as reactive carbon—halogen bonds, giving acid hahdes (7) and into active acid haUdes giving haUdes of p-ketoacids (8) (46). Phosgene [77-44-5] (47) and thiophosgene [463-71-8] (48) also react with ketenes. 

COX acid hahdes halocarbonyl -oyl hahde or carbonyl haUde ... 

Acid hahdes, eg, ben2oyl chloride, acetyl chloride, and ben2oyl bromide, have been used to prepare Si—Cl and Si—Br compounds from organosilanes. Acetyl chloride proceeds to higher yield when cataly2ed by aluminum chloride. 

In sulfamation, also termed A/-sulfonation, compounds of the general stmcture R2NSO2H are formed as well as their corresponding salts, acid hahdes, and esters. The reagents are sulfamic acid (amido—sulfuric acid), SO —pyridine complex, SO —tertiary amine complexes, ahphatic amine—SO. adducts, and chlorine isocyanate—SO complexes (3). 

The molecular weight of the polymers is controlled by temperature (for the homopolymer), or by the addition of organic acid anhydrides and acid hahdes (37). Although most of the product is made in the first reactor, the background monomer continues to react in a second reactor which is placed in series with the first. When the reaction is complete, a hindered phenoHc or metal antioxidant is added to improve shelf life and processibiUty. The catalyst is deactivated during steam coagulation, which also removes solvent and unreacted monomer. The cmmbs of water-swoUen product are dried and pressed into bale form. This is the only form in which the mbber is commercially available. The mbber may be converted into a latex form, but this has not found commercial appHcation (38). 

Acid hahdes can also be used in Migita-Kosugi-Stille coupling in this C-C bond formation fhe corresponding ketone is produced. Subjection of a benzoyl chloride derivative prepared in situ to cross-couphng with a vinylstannane provided the desired vinyl ketone which was successfully transformed to a potent COX-2 inhibitor (Scheme 12.99) [201],... 

Esterification. Esters are formed by the reaction of ethanol with inorganic and organic acids, acid anhydrides, and acid hahdes. If the inorganic acid is oxygenated, eg, sulfuric acid, nitric acid, the ester has a carbon—oxygen linkage that is easily hydrolyzed (24—26). 

PAIs can be prepared by the condensation of a monoanhydride of a tricarboxylic acid and a primary diamine. Further PAI can be prepared by tbe reaction of dicarboxylic acid chlorides and diamines. Here, either the diamines or diacid halides already contain imide linkages, or mutatis mutandis, amide linkages. Classical PAI are usually obtained by reacting equimolar amounts of trimellitic acid hahde anhydride and a diamine. ... 

Esters, amides, and acid hahdes are usually named as derivatives of the parent carboxylic acid. Thus, in Table 4.1, you find ethyl propanoate listed under the parent carboxylic acid, propanoic acid. If you have trouble finding a particular ester under the parent carboxylic acid, try looking under the alcohol part of the name. For example, isopentyl acetate is not listed under acetic acid, as expected, but instead is foimd under the alcohol part of the name (see Table 4.1). Fortunately, this handbook has a Synonym Index that nicely locates isopentyl acetate for you in the main part of the handbook. 

As we have mentioned, acid hahdes are the most reactive of the carboxylic acid derivatives, becanse they produce the most stable leaving gronps. Therefore, we can prepare any of the other carboxylic acid derivatives from acid hahdes. So, it is critical that you know how to make an acid halide. It is very common to encounter a synthesis problem where you will need to make an acid hahde at some point in the synthesis. 

Acid anhydrides are almost as reactive as acid hahdes. So, the reactions of acid anhydrides are very similar to the reactions of acid hahdes. Yon just have to train your eyes to see the leaving... 

The carboxylic acid is first converted into an acid halide, which is then converted into an ester. But this begs the question can we achieve the desired transformation in one step That is, can we convert a carboxyhc acid into an ester in just one step, avoiding the need to prepare an acid hahde If we simply try to mix an alcohol and a carboxylic acid, we do not observe a reaction ... 

If we want to halogenate the alpha position of a carboxylic acid, it is possible, but it will require some extra steps. First, we must convert the carboxyhc acid into an acid halide. We do this because the enol of an acid halide will rapidly attack a halogen. Then, in the end, we just convert the acid hahde back into a carboxylic acid ... 

Notice the reagents that we used. We saw the reagent in the first reaction (Br2 and some mild acid— to halogenate a ketone). But to halogenate a carboxyhc acid, we use a different set of reagents. We use Br2 and PBrs, followed by H2O. The function of Br2 and PBrs is to make the acid halide, form the enol, and then have the enol attack Br2. Then, water is used in the last step to convert the acid hahde back into a carboxyhc acid. 

We wiU begin our survey with a reaction that we have actually already seen in a previous chapter. When we learned about carboxyhc acid derivatives (Chapter 6), we saw that you can convert an acid hahde into an amide. For example ... 

The intramolecular acylation of an aromatic compound can be accomplished using a carboxyUc acid rather than the acid hahde. The reaction requires HF to produce the intermediate acyl cation (Section 13.2). 

According to Figure 21.11, this transformation will require a minimum of four synthetic steps (if we are limited to reactions covered in this chapter). First, the alcohol is oxidized to a carboxylic acid, followed by conversion to an acid hahde. The acid hahde is then converted into an amide, followed by reduction to give an amine, as shown ... 

Benzaldehyde can be made from the corresponding acid hahde (benzoyl chloride). 

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